Biocompatible ventricular assist and arrhythmia control device including cardiac compression band-stay-pad assembly

ABSTRACT

A ventricular assist device for a heart includes a compression band-stay-pad assembly for encircling substantially the entire heart perimeter and comprising an elongated band member or chain disposed in a sealed protective structure filled with a lubricating medium. The band member may be fixed at one end and wound upon, or unwound from, a rotatable spool by a drive motor through a speed reducer. Force-transmitting support or stay assemblies are disposed in the protective structure between the band member and a resilient pad assembly for encircling the heart and promoting heart tissue ingrowth therein. The force-transmitting stay assemblies are biased circumferentially, and thus radially outward, by compression return springs disposed therebetween. The resilient pad assembly includes a corrugated surface provided with vertical coil springs, which help prevent damage to heart tissue and facilitate return of the pad assembly to an initial condition, embedded defibrillator electrodes and relatively soft portions to prevent damage to coronary arteries. The device may be constructed so that it can be surgically removed, except for a sealing film and an ingrown pad of the resilient pad assembly, which remain in situ on the heart. A net structure suspended below the device supports the apical portion of the heart.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a biocompatible ventricular assist andarrhythmia control device, and more particularly to a biocompatibleventricular assist and arrhythmia control device comprising a cardiacventricular compression band-stay-pad assembly, for compressing andassisting in the contraction and expansion of one or both heartventricles, without damaging the ventricle.

2. Description of the Prior Art

U.S. Pat. No. 4,925,443, issued May 15, 1990, to Marlin S. Heilman andSteve A. Kolenik, entitled "Biocompatible Ventricular Assist andArrhythmia Control Device", discloses an implantable ventricular assistdevice which includes (1) one or more movable compression assemblies forengaging a ventricle of the heart; (2) an operating mechanism forcyclically actuating the movable compression assemblies and therebyalternately ejecting blood from the ventricle and permitting theventricle to refill; (3) a sensing means to detect adequacy ofventricular stroke volume and/or pressure; (4) a control mechanism toassure adequate ventricular stroke volume by regulating the compressiveforce of the compression assemblies, and also to control pacemaker,cardioverter/defibrillator, and recorder subsystems; and (5) anelectrical power source.

In that patent, each compression assembly includes a contoured pressureplate and a soft contact pad mounted on the interior plate surface forsuturing and/or gluing the compression assembly to the ventricle. Tominimize mechanical stress on the myocardial surface, including thecoronary arteries, the contact pad consists of an elastomer, such assilicone rubber, or a thermoplastic material (Shore A durometer range30-50). To avoid edge stress, the thickness of each contact pad isprogressively reduced toward its periphery. To further reduce stresseson the myocardium, bearings and axles are used to mount the pressureplates on the compression assembly's driving arm; if the contractingheart produces a torquing force, the joint will permit the pressureplate, within specified limits, to follow the natural movement of theheart.

Similarly, to help prevent the edges of the compression assemblypressure plates from creating pressure points which might cause possibledamage to the heart, a related continuation-in-part U.S. patentapplication Ser. No. 07/019,701, filed May 14, 1990, in the names ofMarlin S. Heilman, et al., entitled "Biocompatible Ventricular Assistand Arrhythmia Control Device Including Cardiac Compression Pad andCompression Pad Assembly", now U.S. Pat. No. 5,098,369, disclosesreplacing the contact pad of each compression assembly with a gel-filledcontact pad of special construction which compresses the heart ventriclemore uniformly without damaging the ventricle.

Other previous attempts to provide ventricular assistance have rangedfrom artificial hearts (e.g., the Jarvik-7), to devices which directlypump the blood via an artificial pathway inserted through theventricular wall, to devices which exert pressure on the outside of theheart. Most frequently, these latter pressure-exerting devices involvesome form of flexible bladder within a support structure such thatexpansion of the bladder presses on the ventricle and facilitatesexpulsion of blood. See, for example, U.S. Pat. Nos. 3,233,607 to Bolie;3,279,464 to Kline; 3,587,567 to Schiff; 3,371,662 to Heid et al.;4,048,990 to Goetz; 4,192,293 to Asrican; 3,455,298 to Anstadt;4,690,134 to Snyder; 4,731,076 to Noon et al.; and 4,957,477 toLundback. Another structurally related device (U.S. Pat. No. 4,506,658to Casile) envisions a truncated conical structure of sac-lined rigidpanels separated by contractible and expandable sections, and anotherdevice (U.S. Pat. No. 4,621,617 to Sharma), which is electromagneticallycontrolled, comprises a pair of hinged compression members. Further,U.S. Pat. No. 4,536,893 to Parravicini envisions using two segmentedsacs, selectively fed by a pumping fluid to compress the right and leftventricles separately.

In general, bladder systems usually have various shortcomings. Theseinclude the possibility of catastrophic bladder fluid leakage (as aresult of the fluid pressures involved), a propensity for damaging theheart surface due to poor fixation and/or rubbing of the bladder againstthe heart's surface, and the unnatural convex form presented to theheart's surface during systolic bladder expansion.

Another type of cardiac assist system is designed to compress all orpart of the heart by alternately tightening and releasing a compressionband. For example, one proposed system for body organs (U.S. Pat. No.4,304,225 to Freeman), such as the heart, involves a flexible strapwhich is fixed to a contoured plastic block and passes across the backof the heart. In response to electrical pulses, a motor assemblyalternately reels in and releases the flexible strap, thereby tending toflatten and force fluid from the heart.

The above-mentioned Freeman patent also discloses the use of a tubularcompression sleeve which substantially encircles the heart and whichcomprises a series of interconnected expandable elliptical chambers. Inuse, a liquid solution is pumped into the sleeve from a supply chamber,causing the elliptical chambers to expand radially inward to compressthe heart in its systolic phase. The solution then is released from thesleeve back to a supply chamber, permitting the heart to expand in itsdiastolic phase.

U.S. Pat. No. 4,583,523 to Kleinke and Freeman illustrates a heartassist mechanism which compresses the aorta, rather than a ventricle,and it compresses during the diastolic phase of cardiac contractioninstead of the systolic phase. Other known prior art of interestincludes U.S. Pat. Nos. 3,668,708 to Tindal, 4,167,046 to Portner,4,092,742 to Kantrowitz et al. and 4,291,707 to Heilman, German PatentDocument No. DE-A-2,557,475, British Patent Document No. GB-A-2,060,174and U.S.S.R. Patent Document No. SU-1572646-A1.

SUMMARY OF THE INVENTION

In general, this invention relates to an implantable ventricular assistdevice which may include (1) one or more motor mechanisms for convertingelectrical and/or hydraulic energy to a mechanical motion forconstricting the perimeter about the heart; (2) movable support or"stay" assemblies for transmitting the motor-induced mechanical motioninto a compressive action on the heart's surface; and (3) a pad orinterface assembly between the movable stay assemblies and the surfaceof the heart, the pad assembly serving a number of purposes includingthe minimization of various mechanical stresses that might otherwisedamage the heart and/or coronary arteries.

A presently preferred embodiment of the invention includes aband-stay-pad assembly positionable about at least one heart ventricleand comprising an elongated band member or chain that activates stayassemblies housed in a fluid lubricant-filled chamber. Included is amechanism for fixing one end of the band member essentially againstmovement. Additionally, there is a rotatable support for winding atleast a portion of the band member thereon relative to thelubricant-filled chamber housing the stay assemblies, as a result of theband member having an opposite end connected to the rotatable support,and a reversible drive mechanism for rotating the rotatable support inone direction to wind up the portion of the band member and therebycompress the heart ventricle during a systolic phase thereof, androtating the rotatable support in a reverse direction to unwind theportion of the band member from the rotatable support, to release theheart ventricle during a diastolic phase thereof.

More specifically, the drive mechanism may include a drive motor and aplanetary gear-type speed reducer connected to the rotatable support.The band member, together with the supports or stays, and stay links, aswell as longitudinally extending and circumferentially arranged returnsprings, is encased in a compressible and expandable protectivestructure, which defines the above-mentioned lubricant-filled chamberand which may comprise a partially corrugated and inner foam-surfacedpad or interface assembly that contacts the heart's surface and iscontinuous, for fluid sealing purposes, with a flexible membranedefining an outside surface of the structure. The stay assembliescomprise: (1) the stay links that are slotted for receiving portions ofthe movable band and which are interleaved with band portions so as toprovide an aligned path for the band; (2) the stays, which may pivot andare connected to inner sides of respective ones of the stay links,typically by means of rocking joints; (3) a series of thecircumferentially extending springs that return the band-stay-padassembly to its beginning (end-diastolic) position; and (4)longitudinally and vertically extending force-transmitting springs thatare supported on the pad assembly and respective ones of the pivotingstays, and have opposite end portions which flex outward as theband-stay-pad assembly compresses into the heart's surface. The returnsprings bias the compression band-stay-pad assembly circumferentially,and thus also radially outward, with the pad assembly being preferablysecured to the heart's surface by suturing and/or ingrowth, so thatoutward expansion of the heart, or diastolic filling, is assisted by thesprings.

In other embodiments, the motor-driven chain is replaced by a pluralityof other types of motor mechanisms provided between selected ones of thestays to assist in contraction and expansion of the heart. Theband-stay-pad assembly also may be formed initially with an adjustableportion by which the assembly can be fitted around a patient's heart in"customized" close-fitting relationship, and multiple compression bandsor chains movable in opposite directions may be utilized.

The present invention, as above described, overcomes a number ofobstacles and complications inherent in state-of-the-art devices and asdisclosed in previously issued patents. For example, U.S. Pat. Nos.4,925,443 and 5,098,369 (Heilman et al.) disclose devices which havediscrete compression plates that, although effective for pumpingpurposes, could under certain circumstances pinch the surface of theheart between the edges of the compression plates. The present inventionrepresents an improvement over these devices because it produces a morecomplete enclosure of the heart's surface, obviating the risk ofpinching.

In other known prior art which utilizes a compression band extendingabout only a portion of the heart, the action of the band is to flattenthe heart and either slide on the heart's surface or splint, i.e.,prevent the surface from undergoing a natural shortening or contractionaction. Flattening the heart produces an unnatural bending of theheart's muscle, and the sliding action of the band on the heart'ssurface is abrasive. The band-stay-pad invention described herein alsois advantageous over these type devices in that it eliminates hardsurfaces or edges being in contact with the heart so as to avoidpinching, while also avoiding flattening or shearing of the hearttissue.

Further, with the subject invention, the bottom or apical portion of theheart is supported by a collapsible net structure having limitedexpansion ability. Should an infarct (death) of the heart's muscle occurfrom a blockage of a coronary artery, the band-stay-pad assembly withits attached net then will provide support and thus avoid or limit anyaneurysmal ballooning or rupture of the heart that otherwise mightoccur.

Many patients suffer from a form of heart failure caused by fibrousreplacement of heart muscle tissue resulting in muscle stiffening. Thepresent invention also is advantageous in this regard in that it has thecapability to both increase heart filling by a slight returnspring-induced stretch during diastole, and increase the depth ofcontraction during systole, and therefore heart emptying, thusovercoming the effects of the abnormal heart muscle stiffness.

From the standpoint of space requirements in the patient's body, theventricular assist device of the present invention also is advantageousin that it has the form of a flexible envelope that fits in the naturalcleavage plane about the heart, with the envelope's attached motor drivefitting, for example, in the natural cleavage plane between thediaphragm and the lower lobe surface of the left lung. Because of thesedesirable fit properties and the relatively small size of the device,surgical complications also are expected to be less than with otherknown assist devices.

The pad assembly, which defines an inner lining of the invention,comprises an inner foam pad having a sealing film on an outer corrugatedsurface, and has a number of other unique features. For example, it isformed in a fashion and will be acted upon by the stay assemblies so asto shrink in the circumferential dimension much the same as the heartsurface does naturally. This action, together with the porosity of itsfoam surface, will promote tissue ingrowth and adhesion of the pad tothe heart's surface, thus avoiding shear stress at the pad-heart surfaceinterface. The foam pad also can be made to possess a degree ofhardness, Shore A 30-50, that is similar to that of heart muscle, thusfurther avoiding unnecessary stress.

By embedding metallic cables constructed of numerous small diameterwires in the corrugated porous foam pad, it also is possible toeffectively create large surface area defibrillating electrodes sincethe foam porosity will allow electric current to flow and the small wirediameters will resist flex-fracturing. The corrugated sealing film onthe stay assembly side of the pad assembly also is sufficiently thin(less than 20 mils) to avoid fatigue fracture from millions ofcompression cycles and may be constructed of multiple layers securedtogether along their upper and lower edges, with only the innermostlayer bonded to the foam pad, and only the outermost layer adjacent tothe stay assemblies sealed to edges of the outside surface membrane forretaining the fluid lubricant. Then, should it be necessary tosurgically replace the band-stay portion of the device, it also is anoption to leave in place the innermost film and the foam pad, which hasbecome connected to the heart by tissue ingrowth. A replacement devicethen would have its own fluid-sealing layer of corrugated film thatwould mate with and be suitably attached to the in situ film layersecured to the foam pad. The compression band-stay-pad assembly and ahousing of the drive mechanism may be filled with a biocompatiblemedium, such as mineral oil, which functions as the above-mentionedfluid lubricant and also prevents body fluids from seeping into thedevice.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram of a ventricular assist device inaccordance with a first embodiment of the invention;.

FIG. 2 is a schematic general front elevational view of the upperportion of a patient's body showing the ventricular assist deviceimplanted on the heart, with the heart shown in its diastolic phase;

FIG. 3 is a schematic view showing the patient's heart and theventricular assist device during a systolic phase of the heart;

FIG. 4A is an enlarged elevational view, partially in cross section,illustrating in greater detail the ventricular assist device attached tothe patient's heart;

FIG. 4B is an exploded view of a plurality of parts of the ventricularassist device;

FIG. 4C is a schematic elevational view of certain parts as shown inFIG. 4B, as seen in the direction of the arrows 4C--4C;

FIG. 4D is a cross-sectional view of one of the parts shown in FIG. 4C,taken along the line 4D--4D;

FIG. 4E is a cross-sectional view of another of the parts shown in FIG.4C, taken along the line 4E--4E;

FIG. 4F is a cross-sectional view of the parts shown in FIGS. 4D and 4Ein assembled relationship;

FIG. 5 is a schematic cross-sectional view, with certain parts omitted,taken essentially along the line 5--5 in FIG. 4A;

FIG. 6 is an enlarged cross-sectional view of a portion of FIG. 5;

FIG. 7A is a cross-sectional view taken essentially along the line7A--7A in FIG. 6;

FIGS. 7B and 7C are schematic views illustrating removal and securingsteps in a device replacement procedure;

FIG. 8A is a partial top view of a second embodiment of the invention,partially in cross-section;

FIG. 8B is an enlarged, elevational view as seen essentially along theline 8B--8B in FIG. 8A;

FIG. 8C is a cross-sectional view taken along the line 8C--8C in FIG.8B;

FIG. 9 is a partial elevational and cross-sectional view of a thirdembodiment of the invention;

FIG. 10 is a schematic, elevational and cross-sectional view of acompression band operating mechanism of the ventricular assist deviceshown in FIGS. 1-7;

FIG. 11 is a cross-sectional view of the compression band operatingmechanism taken essentially along the line 11--11 in FIG. 10;

FIG. 12A is a partial elevational view, partially in cross-section, ofan end portion of an operating chain for a ventricular assist device inaccordance with the invention shown in FIGS. 1-7;

FIG. 12B is a plan view of the end portion of the operating chain shownin FIG. 12A;

FIG. 13A is a schematic, partial cross-sectional view of a fourthembodiment of the invention, taken essentially along the line 13A--13Ain FIG. 13B;

FIG. 13B is a schematic, partial cross-sectional view, with certainparts omitted, taken essentially along the line 13B-13B in FIG. 13A;

FIG. 14A is a schematic, partial cross-sectional view of a fifthembodiment of the invention, taken essentially along the line 14A--14Ain FIG. 14B;

FIG. 14B is a schematic view, partially in cross-section, takenessentially along the line 14B--14B in FIG. 14A;

FIG. 14C is a schematic elevational view as seen essentially along theline 14C--14C in FIG. 14A; and

FIG. 15 is a schematic cross-sectional view illustrating a sixthembodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 discloses a block diagram of a biocompatible ventricular assistand arrhythmia control device 20 in accordance with a first embodimentof the invention, hereinafter referred to as the ventricular assistdevice, it being understood that numerous other variations of theinvention are, of course, possible. As disclosed in FIG. 1, theventricular assist device 20, which operates in synchronism with a heart22, comprises an implantable subsystem 24 and a subsystem 26 externalto, and without penetrating, a patient user's skin 28. The implantablesubsystem 24 includes a direct cardiac energy converter and cardiacpumping mechanism 30 which includes a heart compression band-stay-padassembly 32, and a drive mechanism 34 comprising a rotatable supportspool 36 for winding a band member or chain 38 of the band-stay-padassembly thereon, and unwinding the band member therefrom, a drive motor40, a speed reducer 42 connected between the drive motor and therotatable support spool, and a housing 44 in which the rotatable supportspool, drive motor and speed reducer are mounted. The drive motor 40,through the speed reducer 42 and the rotatable support spool 36,mechanically initiates radially inward ventricle-assist motion of thecompression band-stay-pad assembly 32 when the heart 22 begins tocontract, limits and controls the degree of mechanical compression, andterminates the degree of compression so that the compressionband-stay-pad assembly may return to its original radially outwardposition as the heart refills. The housing 44 is at least partiallyencapsulated in a casing 46 of a suitable biocompatible material, suchas titanium, SILASTIC® silicone elastomer (Dow Corning Corp., Midland,Mich.) or DURAFLEX™ polyurethane (Vascor, Inc., Pittsburgh, Pa.). Theenergy converter and cardiac pumping mechanism 30 also includes sensors(not shown) which provide input to a microcomputer based systemcontroller 48, within an electronic control system module 50 implantablein the patient's body remote from the energy converter and cardiacpumping mechanism, as illustrated in FIG. 2.

The electronic control system module 50, in addition to themicrocomputer based system controller 48, includes a telemetrycontroller 52, an internal transcutaneous energy transmission (TET)controller 54, internal batteries 56, a switching power supply 58, apower monitor 60 and an audible alarm 62. The electronic control systemmodule 50 further includes a cardiac pacer system 64 comprising anautomatic gain controlled (AGC) R-wave or QRS complex (electrocardiogramwaveform just prior to systolic contraction) detector circuit 66, and aprogrammable pacer 68 connected to an electrocardiogram (ECG)/pacer lead70 positionable upon the patient's heart 22 in a known manner. Acardioversion/defibrillation pulse generator 72 also is connected to oneor more defibrillation electrodes 74 also mountable upon the patient'sheart as subsequently discussed with reference to FIGS. 4A and 5. Thecontroller 48 may be connected to the energy converter-and-cardiacpumping mechanism 30 by a system including a preload force interface 76connected to a dedicated force transducer 77 of the compressionband-stay-pad assembly 32, an absolute motor position sensor 78, and apulse width modulated (PWM) motor drive interface 80.

Power is transmitted from the external subsystem 26 to the electroniccontrol system 50 by a patient-worn TET controller 86 and the internalTET controller 54. External power is provided by either a patient-wornbattery pack 88 or a stationary power supply 90. When the battery pack88 is expended, it may be recharged with a battery charger 91. Inaddition, a system programmer 92 may be selectively connected to thepatient-worn TET controller 86 for programming and interrogation.

The programmer 92 may comprise a programmed personal computer system ofa known type, the details of which are not shown, which includes a smallprinter/plotter, a transtelephonic data transmission device and an ACpower supply, with battery backup. A series of menus, displayed on acomputer screen, prompt the operator to select the desired systemcontrol parameters at a keyboard. All selected programming options areautomatically logged at the printer and stored on a 3.5 inch floppydisk. Additionally, when commanded, the programmer 92 will display,record and plot two selected real-time signals (ECG, refractory pulse,motor torque, compression band position, or band velocity) for aselectable time period, such as 2.5 or 5.0 seconds.

FIG. 2 shows the ventricular assist device 20, essentially asrepresented by the block diagram of FIG. 1, with the internal subsystem30 implanted in an upper portion of a patient's body for assisting theheart 22 in the pumping of blood from the heart, through its majorartery (aorta) 94, and to the arterial system. In the disclosedarrangement the energy converter and cardiac pumping mechanism 30 islocated adjacent a heart left ventricle 96, between the patient'sdiaphragm or inside the chest wall of the patient, and the lower lobesurface of the left lung, with the compression band-stay-pad assembly 32fitting in a natural cleavage plane about the heart, and encircling theheart. The electronic control system module 50 is implanted adjacent thewaist of the patient user and is connected to the energy converter andcardiac pump mechanism 30 via a communications and power supply link 98.The external patient-worn TET controller 86 and battery pack 88 aredisposed in a belt 100 which may be worn around the patient user's waistinside or externally of the patient user's clothing and which may beremovably secured by a quick-releasable material of a known type atopposite ends of the belt. The TET controller 86 and battery pack 88preferably are distributed in the belt 100 around a substantial portionof the belt for the patient's comfort. The above-mentioned programmingof the implanted electronic control system 50 can be accomplished fromthe programming device 92 (FIG. 1), by connecting the programming deviceto the patient-worn TET controller 86 via a cord and plug assembly (notshown) insertable into a plug receptacle 102 (FIG. 2) on the belt 100.The recharging of the patient-worn battery pack 88 may be accomplishedby removing the battery pack or the belt 100 for a recharging operationby the battery charger 91, and replacing the battery pack with a fullycharged battery pack, or replacing the belt with a belt having a fullycharged battery pack, to provide continuous, tether-free operation.

Referring to FIGS. 4A, B and C, and FIG. 5, the compressionband-stay-pad assembly 32 comprises the elongated band member or chain38, which may be in the form of a pivoted link chain of a suitablematerial, such as a composite plastic compound like carbon reinforcedpolyphenylene sulfide (PPS), or carbon reinforced polyether ketone. Forexample, the carbon reinforced polyphenylene sulfide (PPS) may be aninjection molded plastic composite including polyphenylene sulfide,TEFLON®, carbon fibers and silicone, available from LNP EngineeringPlastics of Exton, Pa. The chain material also may be a metal, e.g., acobalt based alloy such as that available from SPS Technologies, Inc.,of Jenkingtown, Pa. under the trademark MP35N, or that available fromEligloy Limited Partnership of Elgin, Ill., under the trademark ELIGLOY,a stainless steel (316L), titanium, or a composite of PPS and metal. Theelongated band member or chain 38 also is encased in a protectivestructure 106 of the band-stay-pad assembly 32 for preventing damage tothe heart 22 and/or surrounding tissue.

The compression band-stay-pad assembly 32 further comprises a pluralityof C-shaped rigid support or "stay" members 108, preferably supportedcentrally for rocking movement on respective alternating channel-shapedstay link members 110 and 111, by bearing portions 108b, 110b and 111b(FIG. 4B), respectively, and associated hinge or pivot pins 112. Thestays 108 have enlarged relatively wide end portions 108w (best shown inFIGS. 5 and 6) each provided with a pair of apertures 108a for receivingrespective ends of circumferentially extending, compression-return coilsprings 114, and also have relatively narrow force-transmitting portions108n. Alternatively, the return springs 114 may be mounted on enlargedportions of the stay links 110 and 111. The stays 108, and the staylinks 110 and 111, may be formed of a biocompatible metal, such ascommercially pure titanium or a titanium alloy (e.g., Ti-6AL-4V), or theabovementioned injection molded plastic composite used for the chain 38.

The stay links 110 and 111 provide a mechanism by which the stay members108 and the link chain 38 are supported in adjacent relationship. Forthis purpose, vertically spaced, horizontal legs 110h (FIGS. 4B, C andD) of each stay link 110 are formed with elongated slots 110s (bestshown in FIG. 4D) disposed at an angle 110a on the order of 61/3° to alongitudinal axis of the legs. Each of the stay links 111 includeshorizontal legs 111h having opposite end portions which receive adjacentend portions of the stay links 110 therebetween. The legs 111h includeapertures 111a by which these legs are connected to the legs 110h of thestay links 110 by suitable pins 115 having cylindrical portions 115c(FIG. 4F) fixedly mounted in the apertures and also having rectangularportions 115r disposed for sliding movement in the slots 110s foralignment control. In operation, with reference to FIG. 4F, the staylinks 110 and 111 move between solid line positions (diastole) andbroken line positions (systole).

Referring to FIG. 4C, the legs 110h and 111h of the stay links 110 and111 are disposed on upper and lower sides of the chain 38, whichcomprises chain members 116 having horizontal legs 116h and centralportions 116c received between respective ones of the horizontal legs,with the chain riding on arcuate bearing surfaces 117 (FIG. 4B) of thestay links. As is also shown in FIGS. 12A and 12B, the chain members 116are pivotally interconnected by pins 118 having opposite ends fixed inapertures 120 in the horizontal legs 116h, and intermediate portionsjournaled in suitable bearings 122 in the central portions 116c. Thechain members 116 may be formed of a suitable plastic composite or ametal, as noted previously. Other chain configurations also may be used,such as miniaturized bicycle-type chains, but to minimize wear at thechain-engaging surfaces 117 of the stay links 110 and 111, the stay linksurfaces should be plastic if the surfaces of the chain 38 are metal ormetal if the chain surfaces are plastic.

With further reference to FIGS. 4A and 5, the structure comprising thestays 108, the stay links 110 and 111, and the associated portion of thechain 38, is encased by a sheath assembly 124 comprising an inner pad orinterface assembly 126 and an outer membrane 128. To prevent excessivepressure on main heart coronary arteries 129a and 129b (see FIGS. 2, 3,4A and 5) during the systole phase of the heart 22, a pressure pad 130of the inner pad assembly 126 preferably is formed in two essentiallysemi-circular segments having opposed ends separated by first and secondtubular portions 132 and 134, respectively, as shown in FIG. 5, whichare formed of a relatively softer foam material, and which are suitablysealed closed at their upper and lower ends by plug portions 136 (seeFIG. 4A). When the band-stay-pad assembly 32 is positioned on the heart22, the first tubular portion 132 is located over the main coronaryartery 129a (left anterior descending) and the second tubular portion134 is located on the opposite side of the heart 22 over the rightcoronary main artery 129b. Thus, in compression of the heart 22 by theband-stay-pad assembly 32 during the heart's systole phase, therelatively soft tubular portions 132 and 134 cooperate to reduce therelative pressure applied on the main coronary arteries 129a and 129b.

As is shown in FIG. 4A, the bottom or apical portion of the heart 22 issupported by a collapsible, but essentially non-expandable net structure138 having its upper periphery bonded to the underside of the sheathassembly 124 around its perimeter, with the net structure being movableradially inward and outward therewith. Thus, should an infarct (death)of the heart's muscle occur from a blockage of a coronary artery, thenet 138 will provide support and avoid or limit any aneurysmalballooning or rupture of the heart 22 that may otherwise occur. By wayof example, the net structure 138 may be formed from a polyester fiberbundle 138f having a diameter in a range on the order of 0.6 to 2.6 mm,with elongated net openings 138o having short and long dimensions on theorder of 3 mm and 8 mm, respectively.

The pressure pad 130 is formed of a relatively soft material and has asmooth inner surface 130s which is engageable with the heart 22 withoutcausing damage to the heart tissue. The pad material also is of a typewhich can be sutured to the heart 22 and also preferably is relativelyporous in nature to enhance tissue ingrowth and bonding of the pad tothe heart, so that radial expansion of the band-stay-pad assembly 32assists in expansion of the heart during its diastole phase. Forexample, a suitable material for this purpose is polyurethane foam, atleast the inner heart-contacting surface 130s of which has been treatedwith an anti-microbial agent, such as cephalosporin.

As is shown in FIG. 6, an outwardly facing surface of the compressionpad 130 is of corrugated construction and has a fluid sealing film layer140, such as of polyurethane, bonded thereto by a suitable adhesive,such as also polyurethane, with the resultant corrugations formingalternating ridges 142 and valleys 144. Preferably, as is best shown inFIGS. 6 and 7A, a second fluid sealing polyurethane film layer 146 alsooverlays the first sealing film layer 140 in corrugated form, withadjacent upper and lower edge portions 140e and 146e of the film layersadhesively bonded together at upper and lower bond joints 148 and 150,respectively, and with the intervening portions of the layers unbondedto enable subsequent removal of the second layer from the first layer,for replacement of the compression band-stay-pad assembly 32. The upperand lower edge portions 146e of the outer film layer 146 also are bondedto adjacent upper and lower edge portions 128e of the outer membrane 128(which also may be formed of polyurethane), to form a fluid-tightenclosure. The resultant enclosure 128, 146, together with the drivemechanism housing 44, may be filled (such as through a suitable openingin the housing) with an inert lubricating medium 151, such as mineraloil, which also prevents body fluids from entering the ventricularassist device 20.

Referring to FIG. 6, the narrow portions 108n of the stay members 108,which have arcuate inner surfaces 108i, as shown in FIG. 7A, aredisposed in respective ones of the valleys 144 formed by the corrugatedpad assembly 126, for applying radially inward pressure on the padassembly, and thus the heart 22, during its systole phase. Further, formore precise pressure control and to provide force transmission so as tofurther reduce the possibility of damage to the heart tissue or the padassembly 126 by sharp edges or corners of the stays 108, as is bestshown in FIG. 7A, a longitudinally and vertically extending coil spring152 of circular cross-section and relatively small diameter, such as0.16"±0.080", is disposed between each stay 108 and the outermost filmlayer 146 of the pad assembly 126, with the spring being adhesivelybonded adjacent its center to the stay and along its length to the filmlayer.

Thus, as the stay 108 and the spring 152 move radially inward during aheart compression operation, in which the stay tends to move radiallyinward from a solid line position in FIG. 7A, the stay also tends torotate slightly counterclockwise into a position as illustrated bybroken lines in that figure as a result of the taper of the heart 22.Accordingly, the opposite end portions of the spring 152 tend to flexoutwardly, from a slightly concave solid line position, to a convexposition, as also shown by broken lines in FIG. 7A, with the padassembly 126 adapting to this movement without damage to the padassembly and/or the heart 22. Subsequently, when the stay 108 returns toits initial solid line position in FIG. 7A, during the diastole phase ofthe heart 22, the tendency of the spring 152 to return to its initialposition facilitates restoration of the pad assembly 126, and thus theheart, to which it is secured, to their initial (diastole) conditions.

With further reference to FIGS. 4A and 5, the abovementioneddefibrillation electrodes 74 may be in the form of a plurality of smallmetallic cables 74c of numerous small diameter wires embedded in thefoam pad 130 between the valleys 144 (FIG. 5) of the pad assembly 126,with lower ends of the cables being connected by lead wires of a smallconnector cable 153 (FIG. 4A) to the defibrillation pulse generator 72(FIG. 1). The embedded cables 74c thus function effectively as largesurface area defibrillating electrodes since the porosity of the foampad 130 allows electric current to flow through to the heart 22 whilethe flexibility and strength of the small diameter wires of the cableseffectively resist flex-fracturing.

As is best shown in FIG. 5, one end of the chain 38 is fixedly connectedto the housing 44 of the energy converter and cardiac pumping mechanism30, such as by a pin 153. The other end of the chain 38 is secured tothe rotatable support spool 36, such as by a suitable lug-and-pinconnection 154, so that the chain 38 can be wound thereon, or unwoundtherefrom. Opposite end ones of the stay links 111 also are pivotallyconnected to lug portions of the motor housing 44 by respectiveconnector pins 155 and 156. Thus, during winding of the chain 38 uponthe rotatable support spool 36, and unwinding of the chain therefrom, tocause alternate contraction and expansion of the compressionband-stay-pad assembly 32, the chain or band moves longitudinally tocause radially inward and outward movement of the stays 108, springs 152and the compression pad assembly 126, as previously described.

As is apparent from FIGS. 2, 3, 4A and 5, the band-stay-pad assembly 32,including the motor housing 44, encircles the heart 22 so as to beessentially independent of any other parts of the patient's body forsupport. Further, as is also shown in FIG. 6, the stays 108 are mountedon the chain 38 by the stay links 110 and 111, and are biased apartcircumferentially by their associated return springs 114 so that thecompression band-stay-pad assembly 32, including the motor housing 44,is constantly biased toward a radially outward position. When the chain38 is wound on the support spool 36, however, the diameter of theassembly 32 (including the motor housing) encircling the heart 22, isreduced so that the stays 108 and the stay links 110 and 111 move towardone another circumferentially, compressing the springs 114, with thestays also moving radially inward about the perimeter of the heart toheart-compressing positions. Thus, during the systolic phase of theheart 22, substantially the entire perimeter of the heart (except for asmall portion adjacent the motor housing 44) can be compressedessentially uniformly radially inward, and during the diastolic phase ofthe heart, the heart can expand in a similar manner radially outward.Further, during the latter movement, as a result of the foam pad 130being secured to the heart 22 by suturing and/or ingrowth of the hearttissue, the springs 114, and also the springs 152, assist the heart inreturning to its expanded condition.

FIGS. 7A, 7B and 7C illustrate an above-mentioned feature of theinvention by which essentially the entire compression band-stay-padassembly 32 may be replaced during surgery, leaving the inner foam pad130, which has become ingrown with heart tissue, in situ on the heart.For this purpose, as is illustrated schematically in FIG. 7B, to removethe band-stay-pad assembly 32 while leaving the foam pad 130 in situ, asurgeon may cut the innermost film layer 140, which is bonded to thefoam pad, from the outermost film layer 146 and thus the outer membrane128 in a suitable manner. For example, the surgeon may cut the innermostfilm layer 140 from the outermost film layer 146 along cut lines 157adjacent (but slightly spaced from) the bond joints 148 and 150 (FIG.7A) for the layer edge portions 140e and 146e, whereupon the entirecompression band-stay-pad assembly 32, except for the foam pad 130 andthe innermost film layer 140 bonded thereto, can be removed from theheart 22. Referring to FIG. 7C, remaining opposite end portions 140er ofthe innermost film layer 140 then can be attached to opposite edgeportions 146eR of a replacement compression band-stay-pad assembly (notshown), by suitable bonding and suturing, as illustrated schematicallyin this figure.

FIGS. 8A, B and C illustrate a second embodiment of the invention inwhich the motor-driven compression band-stay-pad assembly 32, includingthe circumferentially extending return springs 114, is replaced by astay-pad assembly 32' comprising a plurality of motor or power assistdevices 158 for respective sets of stays 108'. For example, one of thepower assist devices 158 may be provided for each set of every five ofthe stays 108', as is shown in FIG. 8A.

For this purpose, every fifth or "corner" stay 108' is in the form of atapered, wedge-shaped block member having facing sides of the staysparallel to one another. The next adjacent intermediate stays 108' havea modified C-shape, as is best shown in FIG. 8C, with relatively narrowinner portions and relatively wide outer portions, as is best shown inFIG. 8A. A central stay 108' also is of the modified C-shape, but ofuniform width, as also best shown in FIG. 8A.

In this instance, each power assist device 158 is a double-actinghydraulic actuator or motor having a cylinder member 160 fixed, such asby welding, to one of the corner stays 108', and a piston rod 162similarly secured by welding to the other corner stay of the set. Thus,by selective operation of the actuator 158, the corner stays 108' of theset can forcibly be pulled toward one another to assist in compressionof a heart 22' in its systole phase, and forcibly moved apart during theheart's diastole phase.

Each set of the stays 108' also includes upper and lower guide pins 164extending horizontally through apertures in upper and lower portions ofthe corner stays, intermediate stays and central stays, with the guidepins 164 fixed to the central stays by suitable welding 166, andslidably received in the intermediate stays and the corner stays of theset. Relative movement between the intermediate stays 108' and thecorner stays 108' is limited by retaining members 168 having first endssecured (e.g., welded) to the corner stays and having lost motion slots170 (FIG. 8B) at their opposite ends for receiving projecting pins 172on the intermediate stays. In adjacent sets of the stays 108', as isbest illustrated in FIG. 8B, similar guide pins 174 and retainingmembers 175 also are provided, but are located at different levels thanthe guide pins 164 and retaining members 172, to prevent interferencetherebetween.

As is shown in FIG. 8C, in this embodiment of the invention, each staymember 108' has an innermost inclined planar surface 108i', instead of acurved surface such as the curved surface 108i in the embodiment of theinvention shown in FIGS. 1-7. Thus, a force transmitting small coilspring 152' is, in this instance, of relatively straight construction,and remains essentially so during heart systolic and compression phases,rather than moving between concave and convex positions, as in the caseof the spring 152 of that embodiment. In other respects, the function ofthe spring 152', and an associated pressure pad assembly 126', includinga foam pad 130' and edge-bonded sealing film layers 140' and 146', withthe latter film layer also bonded to an outer membrane 128', isessentially the same as in the previous embodiment.

FIG. 9 discloses a third embodiment of the invention similar to thatdisclosed in FIGS. 8A, B and C, in which each of a plurality of motor orpower assist devices 176 (only one shown) includes a main solenoid 178comprising a cylindrical coil assembly 180 fixedly mounted on one of twocorner stays 108" and a T-shaped actuator mechanism 182, including anarmature portion 184, slidably disposed in the cylindrical coilassembly. The coil assembly 180 also carries a first latching mechanism186 and a projecting outer end of the actuator mechanism 182 includes asecond latching mechanism 188. Upper and lower guide pins 190 also arefixedly mounted in central stays 108" by welding 166", and slidablymounted in both of the corner stays 108" and intermediate stays 108" asin the embodiment of the invention shown in FIGS. 8A, B and C, withguide pins 191 for adjacent sets of the stays similarly mounted atdifferent levels.

The first latching mechanism 186 comprises vertically movable upper andlower latch members 192 slidably mounted for vertical movement on thecoil assembly 180 and having respective upper and lower ends formed withteeth which are selectively engageable in notches of upper and lower barracks 194, respectively. As viewed in FIG. 9, the bar racks 194 arefixed to the right-hand corner stay 108" and slidably received in theleft-hand corner stay 108". The latch members 192 are movable into andout of engagement with the bar racks 194 by respective springs 196 andassociated first small solenoids 198. The second latching mechanism 188similarly comprises upper and lower latch members 200 which are biasedto latching positions by a single return spring 202, and movable out oftheir latching positions by second small operating solenoids 204.

More specifically, at the beginning of a systole phase of a heart (notshown), with the stays 108" in their open positions, the first latchmembers 192 are disengaged from the racks 194 and the second latchmembers 200 are engaged therewith. The main solenoid 178 then isoperated momentarily so that the second latch members 200 move the racks194 and the right-hand corner stay 108" to the left (as viewed in FIG.9) one increment, at which time the first small solenoids 198 aredeenergized so that the springs 196 move the first latch members 192into holding engagement with the racks, whereupon the second smallsolenoids 204 are energized to retract the second latch members 200. Themain solenoid 178 then is deenergized so that a coil return spring 206extends the second latching mechanism 188 for advancing the bar racks194 another increment. Next, the second latch members 200 are releasedby their solenoids 204 so that their return spring 202 moves the latchmembers back into engagement with the racks 194, whereupon the firstlatch members 192 are retracted from rack engagement by their solenoids198. The incrementing process then is repeated until a desired closureof the stays 108" has been achieved, with the process being repeated inreverse for a heart diastole phase.

Referring again to the first embodiment of the invention and FIG. 10,the motor 40 of the energy converter and cardiac pumping mechanism 30includes a fixed stator 208 and a drive shaft 210 extending from a rotor212 coaxial with and partially located within a hollow cylindrical drivemember 214 of the speed reducing mechanism 42. Further, an upper end ofthe motor drive shaft 210 is connected to the speed reducer drive member214 via a planetary gear system 216. The rotatable support spool 36 isfixedly mounted on a lower portion of the speed reducer drive member 214in a suitable manner, also not shown.

Referring to FIGS. 10 and 11, an upper end of the drive motor shaft 210includes a gear 218 which forms a sun gear of a lower planetary gearsystem 220, with the sun gear being drivingly engaged with threeplanetary gears 222 (see FIG. 11), in turn engaged with a ring gear 224fixedly mounted to the interior of the hollow speed reducer drive member214. The planetary gears 222 are mounted for rotation on vertical shafts226 secured at their upper ends to respective arms 228 of a supportmember 230 having at its center a vertical shaft 232 upon which a secondsun gear 234 of an upper planetary gear system 236 is fixedly mounted.As is shown in FIG. 10, the second sun gear 234 also is drivinglyengaged with three planetary gears 238, in turn engaged with a secondring gear 240 fixedly mounted to the interior of the hollow speedreducer drive member 214. The second planetary gears 238 also arerotatably supported on depending shafts 242 mounted at their upper endsin a top wall of the housing 44. Thus, operation of the motor 40 in onedirection causes winding of the compression band or chain 38 on therotatable support spool 36 to wind the band thereon and cause inwardradial movement of the compression band-stay-pad assembly 32 to assistthe heart 22 in its systole phase, and operation of the motor in thereverse direction permits unwinding of the band from the rotatablesupport member to permit the abovementioned radially outward expansionof the compression band-stay-pad assembly during the diastole phase ofthe heart.

FIGS. 12A and B illustrate the construction of the end wrapping portionof the link chain 38 which is secured to the rotatable support spool 36and wound upon the support spool to contract the compressionband-stay-pad assembly 32 during a heart systolic phase, and thenunwound from the support spool to permit the compression assembly toretract outward in a heart diastolic phase. In this connection, thisportion of the chain 38 is of essentially the same construction as thecompression portion of the chain previously described, comprising aseries of chain link members 116 interconnected by pivot pins 118 fixedat upper and lower ends in the apertures 120 in the link member legs116h, and having intermediate portions journaled in the wear-resistantcylindrical bearings 122 in the link member central portions 116c,except that the end link member is adapted to be connected to therotatable support spool by the pin 154. Further, inner surface portions116s of the chain members 116 which engage against the support spool 36are formed with a curved radius, such as one inch, to facilitate thewinding of the chain members on the support spool.

A fourth embodiment of the invention, as disclosed in FIGS. 13A and 13B,is of similar construction to the first embodiment of the invention, asdisclosed in FIGS. 2-7C. In this connection, this embodiment includes acompression band-stay-pad assembly 32-4, comprising a series of arcuatestay members 108-4 mounted for pivoted rocking movement on alternatingstay link members 110-4 and 111-4 by pivoted connections 110b-4 and111b-4, with the stay members being provided with curved coil springs152-4. An end one of the stay link members 111-4 is pivotally connectedto a fixed member 246 on a housing 44-4 of a drive mechanism 34-4, by aconnector pin 155-4, and an opposite end one of the stay link members issimilarly connected to the fixed member 246 by a connector pin 156-4. Acompression band, in the form of a chain 38-4, encircles the stay linkmembers 110-4 and 111-4, with the chain being fixedly connected at oneend on the fixed member 246 by a connector 153-4, and connected at itsopposite end, by a connector 154-4, to a rotatable support spool 36-4 ofthe drive mechanism 34-4. The foregoing assembly is encased in aprotective structure 106-4 filled with a lubricating medium andcomprising a pad assembly 126-4 and an outer membrane 128-4, with thehousing 44-4 also encased in a suitable biocompatible casing 46-4.

The embodiment of FIGS. 13A and 13B differs from the embodiment of FIGS.2-7C in that the stay members 108-4 are of circular cross-section,rather than of a relatively complex configuration as disclosed in thatembodiment. Further, rather than the compression band-stay-pad assembly32-4 being circumferentially biased by the springs 114 between the staymembers 108, this biasing is achieved by springs 114-4 disposed in slots110s-4 in the stay link members 110-4, with the springs being locatedbetween end portions of hinge pins 112-4, for interconnecting these staylink members with the stay link members 111-4, and opposite ends of theslots. To retain the springs 114-4 in the slots 110s-4, the upper andlower legs 110h of the stay link members 110-4 are provided with covermembers 248, secured thereon in a suitable manner, such as by welding orsmall screws (not shown). Further, since in this embodiment the staylink members 110-4 and 111-4 tend to close together to a greater degreeduring a heart contraction-assist operation, than the stay link members110 and 111 in the embodiment of FIGS. 2-7C, if all of the stay linkmembers were provided with the arcuate bearing surfaces 117, thesurfaces would interfere with one another during a closing operation;accordingly, in this embodiment only the stay link members 111-4 areprovided with arcuate bearing surfaces 117-4 for supporting the chain38-4 during its movement relative to the stay link members, with thestay link members 110-4 being of a modified construction as shown. Inother respects, the structure and operation of the embodiment of FIGS.13A and 13B is essentially identical to the embodiment of the inventiondisclosed in FIGS. 2-7C.

FIGS. 14A, B and C disclose a fifth embodiment of the invention in whicha compression band-stay-pad assembly 32-5 is constructed in the form oftwo essentially arc-shaped portions 250 each connected to a drivemechanism 34-5 at one end (right-hand in FIGS. 14A and B) and initiallyunconnected at an opposite end (left-hand in FIGS. 14A and B) andseparated so as to provide an adjustable portion 32-5A, so that thecompression band-stay-pad assembly can be adjusted to size as it isfitted to a patient's heart 22-5, and thus "customized" depending uponsize of the heart. Further, in this embodiment, rather than being movedinto a heart contracting-assist condition (systole) by a single chainsecured at one end and wound up at its opposite end, the compressionband-stay-pad assembly 32-5 is contracted by multiple chains being woundup in opposite directions simultaneously.

For this purpose, as is best shown in FIG. 14C, a net structure 138-5for supporting an apical portion of the heart 22-5 is provided on thecompression band-stay-pad assembly 32-5, as disclosed in the firstembodiment of the invention in FIGS. 3 and 4A, with parts 252 of the netbeing extended upward between the adjacent initially unconnected ends ofthe compression band-stay-pad assembly, suitably secured to the adjacentinitially unconnected ends, and having partially overlapping portions252-0. The parts 252 of the net 32-5 then may be used by a surgeon topull the compression band-stay-pad assembly 32-5 into tight-fittingrelationship with respect to the heart 22-5 when it is in its diastolicphase, whereupon the overlapped portions 252-0 may be suitably securedtogether. Thus, the compression band-stay-pad assembly 32-5 can be"custom-fit" to the heart 22-5, as noted previously.

Further, to contract the thus "customized" compression band-stay-padassembly 32-5 about the heart 22-5 in its systolic phase, a pair ofupper and lower chains 38-5A and an intermediate chain 38-5B movabletherebetween adjacent a drive mechanism 34-5, are provided. In thisinstance, the drive mechanism 34-5 is of a hydraulic type and comprisesupper and lower housing members 254 and an intermediate housing member256 capable of free rotation in a casing 46-5 which is filled withlubricant as a result of being in fluid communication with the adjacentends of the compression band-stay-pad assembly 32-5. A vertical shaft258 extends downwardly through the housing members 254 and 256, with theupper and lower housings 254 being fixedly mounted to upper and lowerend portions of the shaft, respectively. Fixed to an intermediateportion of the shaft 258 is a vane member 260 which is movable in anarcuate inner chamber 262 within the intermediate housing 256, with theintermediate housing being rotatably mounted on the shaft by suitablebearings 264, and with the arcuate inner chamber 262 being ofliquid-tight construction as a result of suitable seals 266 encirclingthe shaft at upper and lower ends of the chamber.

A liquid inlet line 268 and a liquid outlet line 270 also are suitablyconnected to the upper end of the shaft 258, with the inlet line feedingvertically downward through the shaft and opening into the inner chamber262 of the intermediate housing 256 between the vane 260 and an adjacentchamber wall 272. Similarly, the outlet line 270 extends downwardthrough the shaft 258 and opens into the inner chamber 262 on anopposite side of the vane 260. The upper and lower chains 38-5A aresecured to respective ones of the upper and lower housings 254 byconnectors 154-5A (one shown in FIG. 14A for the upper chain), and theintermediate chain 38-5B is similarly secured by a connector 154-5B(FIG. 14A) to the intermediate housing 256. The inlet and outlet lines268 and 270 also are connected to a liquid source, comprising a pump anda storage chamber, not shown.

Thus, in operation, when liquid is introduced through the inlet line 268into the inner chamber 262 of the intermediate housing 256 between thevane 260 and the adjacent inner wall 272, opposing thrust forces arecreated on the vane and the inner wall causing the vane and the shaft258 to which it is secured, to rotate clockwise as viewed in FIG. 14A,while at the same time the intermediate housing is caused to rotate inan opposite direction counterclockwise in this figure. Further, sincethe upper and lower housings 254 are fixed to the vertical shaft 258,these housings also tend to rotate clockwise in FIG. 14A. Thus, theupper and lower chains 38-5A are wrapped upon their respective upper andlower housings 254 in a clockwise direction, while the intermediatechain 38-5B is wrapped upon the intermediate housing 256 in acounterclockwise direction, to cause contraction of the band-stay-padassembly 32-5 about the heart 22-5 during its systolic phase.

FIG. 15 discloses a sixth embodiment of the invention, which, like theembodiment of the invention shown in FIGS. 14A, B and C, can be"custom-fit" to a patient's heart 22-6. In this instance, however, acompression band-stay-pad assembly 32-6 extends essentially around theentire periphery of the heart 22-6, with an adjustable portion 32-6A ofthe assembly being provided between a drive mechanism 34-6 at one end ofthe assembly, and an opposite end thereof. Thus, in this embodiment, asin the embodiment of the invention of FIGS. 14A, B and C, the"custom-fitting" of the compression band-stay-pad assembly 32-6 to theheart 22-6 can be accomplished by utilizing upwardly extending portions274 of a net structure (not shown) for supporting an apical portion ofthe heart as disclosed in those figures. In this embodiment, however,only a single chain 38-6 is provided with the chain being wound up bythe drive mechanism 34-6 in a clockwise direction, as indicated by thesolid-line arrow in this figure. In the alternative, an adjustableportion 32-6A of the compression band-stay-pad assembly 32-6 may beprovided adjacent the opposite side of the drive mechanism 34-6, asillustrated by broken lines, with the aforementioned chain then beingwound up in a counter clockwise direction, as indicated by the brokenline arrow in this figure.

In general, referring again to FIG. 1, in operation, the energyconverter and cardiac pumping mechanism 30 converts electrical powersignals, received from the electronic control system 50, to directmechanical cardiac assist by the compression band-stay-pad assembly 32.Typically, data and power are transcutaneously transferred from theexternal controller 86 and battery pack 88 to the implanted electroniccontrol system 50. The external battery pack 88 also can be selectivelyrecharged by the battery charger 91, and periodic system programming canbe accomplished by temporarily connecting the external controller 86 tothe programmer 92. The internal batteries 56, contained in theelectronic control system 50, provide system power for periods when thebelt 100 (FIG. 2) containing the external controller/battery pack 86, 88is temporarily removed by the patient user. In the alternative, thepower line-operated stationary power supply 90 may be used in place ofthe patient-worn battery pack 88.

With further reference to FIG. 1, the electronic control system 50regulates fundamental cardiac assist, pacer andcardioverter/defibrillation functions. In the normal operating mode, theelectronic control system 50 monitors the electrocardiogram (ECG) signalreceived by the detector 66 from the ECG/pacer lead 70. Upon thedetector circuit 66 detecting a ventricular contraction initiation(R-wave or QRS complex), a programmable delay period is initiated afterwhich the motor 40 is driven forward causing the compressionband-stay-pad assembly 32 to compress the myocardium of the heart 22.When the systolic cycle is complete, the motor 40 is returned to its enddiastolic position, causing and/or permitting the compressionband-stay-pad assembly 32 to expand radially outward.

In a pre-systolic phase, approximately 30 milliseconds before the nextanticipated QRS complex (predicted by analyzing previous R to Rintervals) a light preload pressure (programmable) is applied to theheart 22. This pressure minimizes mechanical shock loading andmyocardial impact during the initial phase of the impending systolicassist cycle. At the same time, the electronic control system 50 alsocontrols the pacer 68 and the defibrillator pulse generator 72.

With further reference to the pre-systolic phase, approximately 30milliseconds prior to the next anticipated systolic cycle, the motor 40is driven forward a programmed fixed amount. The arrival time of systoleis predicted by storing the four most recent cycle periods with theshortest of the four periods being used to predict the onset of theimpending cycle. If the current end diastolic position was setcorrectly, the compression band-stay-pad assembly 32 then should begincompressing the myocardium during the second half of the pre-systolicmotor travel. A corresponding increase in the drive current of the motor40 then will be required to finish the motor's travel in thepre-systolic phase and motor current may be monitored by the PWM motordrive circuit 80. However, if an increase in current is not observed bythe controller 54, the end diastolic position of the compressionband-stay-pad assembly 32 then will subsequently be modified (increased)to provide a "tighter" (more radially inward) end diastolic position, inpreparation for the next systolic phase. Similarly, if a high motordrive current is observed by the controller 54 throughout thepre-systolic travel period of the motor 40, the end diastolic positionwill subsequently be modified (decreased) to provide a "looser" (moreradially outward) end diastolic position of the compressionband-stay-pad assembly 32. As an alternative, or in addition tomonitoring motor current, the preload force interface 76 and the forcetransducer 77 may be used to directly measure the cardiac force exertedby the compression band-stay-pad assembly 32, and modify the enddiastolic position accordingly. Other force-indicative parameters alsomay be measured and used for this purpose.

Typically, while as previously discussed, the systolic assist phaseshown in FIG. 3 is triggered when a QRS complex is detected, an assistescape interval, such as 833 milliseconds, may also be programmed andenabled. The assist escape interval triggers the systolic assist phase(and a pacer pulse is output if the pacer 68 is enabled) if a QRS signalis not detected within a preselected time interval, or if there iscontinuous sensing of noise during the interval such that the QRS signalcannot be detected, thus effectively providing asynchronous assist ifQRS sensing is lost. Alternately, the electronic control system 50 maybe programmed to operate asynchronously at a selected rate (possiblyused during ventricular fibrillation). Again, once the systolic phase istriggered, the programmable delay period is initiated, as previouslydescribed. When the delay period is complete, the motor 40 then isdriven forward causing the compression band-stay-pad assembly 32 tocompress the myocardium of the heart 22.

In summary, a new and improved biocompatible ventricular assist andarrhythmia control device 20 has been disclosed. For example,essentially the entire device 20 can be completely and readily implantedin the body of a patient user, and can operate independently of anexternal source from the battery pack 88 in the belt 100 being wornaround the patient user's waist. The energy converter and cardiacpumping mechanism 30, including the compression band-stay-pad assembly32, which can be secured directly to the patient user's heart 22, alsoprovides a system which helps ensure positive compression and expansionassistance to the heart during its systolic and diastolic phases,respectively. During the systolic phase, the heart-engaging foam pad130, film layers 140 and 146 and the force-transmitting vertical springs152 cooperate to prevent damage to the heart. Further, theheart-engaging foam pad 130, the stay members 108, the circumferentiallyextending return springs 114 and the force-transmitting vertical springs152, cooperate to facilitate the heart's expansion during the diastolicphase. As is illustrated in FIGS. 7A, B and C, the provision of theinner and outer film layers 140 and 146 on the foam pad 130 also enablesremoval of the compression band-stay-pad assembly 32, except for theinner film layer 140 and the foam pad 130 to which it is bonded, whichremain in situ on the heart 22, and then replacing the removed assemblystructure with a new compression band-stay-pad assembly structure.Further, in the invention embodiments of FIGS. 8A, B and C, and FIG. 9,respectively, the hydraulic actuator mechanism 158 and thesolenoid-latch mechanism 176 provide alternative modes of producingheart contraction and expansion assistance, while the embodiments ofFIGS. 13A-15 provide other advantageous features.

It is to be understood that the foregoing description and accompanyingdrawings set forth the preferred embodiments of the invention at thepresent time. Various modifications, additions and alternative designswill, of course, become apparent to those skilled in the art in light ofthe foregoing teachings without departing from the spirit and scope ofthe disclosed invention. Therefore, it should be appreciated that theinvention is not limited to the disclosed embodiments but may bepracticed within the full scope of the appendant claims.

We claim:
 1. A ventricular direct mechanical assist device, whichcomprises:a series of force-transmitting linked members for arrangementaround a perimeter of a portion of a heart; and means for actuating saidmembers to apply compression to the heart; wherein said members receivemechanical energy acting on said members and transmit mechanical energyto the heart.
 2. The device as recited in claim 1, furthercomprising:means for moving said force-transmitting linked members inradial directions; and compression return springs interconnecting saidforce-transmitting linked members.
 3. The device as recited in claim 2,which further comprises means for maintaining said compression returnsprings aligned with each other.
 4. The device as recited in claim 1,further comprising a circumferentially movable band mechanism;whereinsaid force-transmitting linked members receive mechanical energy fromsaid band mechanism through circumferential movement about the perimeterof the heart, thereby exerting force perpendicular to said heartperimeter.
 5. The device as recited in claim 1, wherein at least aportion of said force-transmitting members are interconnected by a powermechanism for exerting at least a closure force perpendicular to andbetween said interconnected members.
 6. The device as recited in claim5, wherein said power mechanism includes a hydraulic cylinder andpiston.
 7. The device as recited in claim 5, wherein said powermechanism is a solenoid actuator.
 8. The device as recited in claim 7,which further comprises latching means for capturing stroke motionsproduced by said solenoid actuator.
 9. The device as recited in claim 1,which further comprises a resilient pad assembly having an outermostcorrugated surface defining alternating ridges and valleys, and whereineach force-transmitting member further includes a longitudinallyextending spring that supports said pad assembly and is received in arespective one of the valleys in the corrugated surface of said padassembly.
 10. The device as recited in claim 9, comprising means forflexing said pad assembly-supporting spring progressively towardsopposite ends thereof during a force-transmitting operation, from adiastolic concave form to a systolic convex form.
 11. A ventricularassist device which can be implanted in a patient user exterior to theheart adjacent at least one ventricle, and which comprises:compressionband means for surrounding the perimeter of the heart and having apreselected perimeter length when the heart is in a diastolic phase;means for shortening the perimeter length when the heart is in asystolic phase; and force-transmitting means for receiving mechanicalenergy from said band means as its perimeter length is shortened andtransmitting said energy to compress the heart in its diastolic phase.12. A ventricular assist device which can be implanted in a patientuser, which comprises:means for actively compressing the patient'sheart; and a collapsible netting structure supporting an apical portionof the heart and connected to said compressing means.
 13. The device asrecited in claim 12, wherein the collapsible netting structure is a netcapable of passive surface area contraction yet incapable of stretchingbeyond a preselected limit.
 14. The device as recited in claim 13,wherein said net is formed from a fiber bundle having a diameter in arange on the order of 0.6 to 2.6 mm in diameter, and has openings havingdimensions of approximately 3 by 8 mm.
 15. The device as recited inclaim 14, wherein said fiber bundle is constructed of polyester.
 16. Aventricular assist device which can be implanted in a patient user,which comprises:a contact surface for contacting the heart; means forcontracting and expanding the contact surface of the assist device; andan electrically-driven motor attached to said means for contracting andexpanding for causing contraction and expansion of said contact surface,said motor further including means for fitting in a natural cleavageplane between the left lung and diaphragm or the left lung and an insidechest wall of the patient.
 17. A ventricular assist device which can beimplanted in a patient user exterior to the heart, comprising:elongatedband means positionable around the entire perimeter of the heart;rotatable support means for winding at least a portion of the band meansthereon and unwinding the portion of the band means therefrom, the bandmeans being connected to the rotatable support means; resilient padmeans for engaging the heart and applying pressure thereto in responseto movement of said band means; means for sensing the systolic anddiastolic phases of the heart; and reversible drive means for rotatingthe rotatable support means in one direction to wind the portion of theband means thereon and thereby compressing the heart ventricle during asystolic phase thereof, and for rotating the rotatable support means ina reverse direction to unwind the portion of the band means from therotatable support means, to release the heart during a diastolic phasethereof.
 18. The ventricular assist device as recited in claim 17,wherein the drive means includes a drive motor and a speed reducerconnected to the rotatable support means.
 19. The ventricular assistdevice as recited in claim 18, wherein the speed reducer includes atleast one planetary gear system connected between the drive motor andthe rotatable support means.
 20. The ventricular assist device asrecited in claim 19, wherein the planetary gear system includes a sungear mounted on a drive shaft of the drive means.
 21. The ventricularassist device as recited in claim 17, wherein the resilient pad means isat least partially of corrugated construction.
 22. The ventricularassist device as recited in claim 17, which further comprises protectivemeans for encasing the band means, the protective means including theresilient pad means.
 23. The ventricular assist device as recited inclaim 22, which further comprises lubricating medium contained in theprotective means.
 24. The ventricular assist device as recited in claim23, wherein the resilient pad means includes a porous member having aheart-engaging surface on an inner side thereof and a sealing film on anouter side thereof.
 25. The ventricular assist device as recited inclaim 24, which further comprises:a second sealing film having oppositeedge portions secured to respective opposite edge portions of saidfirst-mentioned film, with intermediate portions of said films beingunsecured to one another; and a sealing membrane forming part of saidprotective structure and having opposite edge portions also secured tosaid edge portions of said sealing films and cooperating with said filmsto encase said band means.
 26. The ventricular assist device as recitedin claim 25, wherein the resilient pad means includes spring means forreturning the resilient pad means from an end systolic condition to anend diastolic condition.
 27. The ventricular assist device as recited inclaim 26, wherein said spring means are elongated coil springs bonded tosaid resilient pad means.
 28. The ventricular assist device as recitedin claim 17, wherein the resilient pad means includes spring means forreturning the resilient pad means from an end systolic condition to anend diastolic condition.
 29. The ventricular assist device as recited inclaim 17, which further comprises means for slidably supporting saidband means, said support means being formed of plastic when said bandmeans is formed of metal, and being formed of metal when said band meansis formed of plastic.
 30. The ventricular assist device as recited inclaim 17, wherein the band means is a chain.
 31. The ventricular assistdevice as recited in claim 17, which furthercomprises:force-transmitting members disposed between said band meansand said resilient pad means.
 32. The ventricular assist device asrecited in claim 31, which further comprises compression return springsdisposed between respective ones of said force-transmitting members. 33.The ventricular assist device as recited in claim 31, wherein saidforce-transmitting members are each comprised of a plurality of supportmembers, at least some of which have surface means for supporting saidband means for movement relative to said support members.
 34. Theventricular assist device as recited in claim 33, further comprisingpin-and-slot connections, wherein said support members areinterconnected by said pin-and-slot connections so as to be contractibleand expandable circumferentially.
 35. The ventricular assist device asrecited in claim 34, wherein said compression return springs aredisposed in said pin-and-slot connections.
 36. The ventricular assistdevice as recited in claim 17, wherein the band means includes biasingmeans for biasing the band means outward in the diastolic phase of theheart ventricle.
 37. The ventricular assist device as recited in claim36, which further comprises means for securing the band means to theheart ventricle.
 38. The ventricular assist device as recited in claim17, wherein the resilient pad means is formed, at least in part, of asoft porous foam material for engaging the heart.
 39. The ventricularassist device as recited in claim 17, which further comprises:externalcontrol means for controlling the reversible drive meanstranscutaneously; an external battery pack connected to said controlmeans; and a belt adapted to be worn externally by the patient user,said belt housing said control means and said battery pack.
 40. Theventricular assist device as recited in claim 39, which furthercomprises a contractible net means secured to said band means forsupporting the apical portion of the heart, said band length adjustmentmeans comprising portions of said net means extending between opposedportions of said band means and being adapted to be secured together inoverlapped relationship.
 41. The ventricular assist device as recited inclaim 17, which further comprises means for adjusting the length of saidband means.
 42. The ventricular assist device as recited in claim 17,which further comprises means for immovably fixing one end of saidelongated band means, with an opposite end of said band means beingconnected to said reversible drive means.
 43. The ventricular assistdevice as recited in claim 17, wherein:said elongated band meansincludes first compression band means positionable about a portion ofthe heart for heart-contracting movement in a first direction; saidelongated band means further includes second compression band meanspositionable about another portion of the heart for heart-contractingmovement in a second direction; and said reversible drive means includesfirst and second reversible drive means for moving said first and secondcompression band means in their respective directions.
 44. Theventricular assist device as recited in claim 43, wherein one of saidcompression band means comprises a pair of spaced band members and theother of said compression band means comprises a single band membermovable between said spaced band members adjacent said reversible drivemeans.
 45. The ventricular assist device as recited in claim 43, whichfurther comprises means for adjusting the combined circumferentiallength of said first and second compression band means.
 46. Aventricular assist device for direct mechanical assistance to a heart,which comprises:means for sensing systolic and diastolic phases of theheart; means for encircling and contracting the perimeter of a surfaceportion of the heart when the heart is in a diastolic phase; andresilient means for cyclically shortening and lengthening saidencircling means in a perimeter direction during systolic and diastolicphases of the heart, respectively, and for receiving and transmittingmechanical compression force to the surface portion of the heart.